1. Field of the Invention
The present invention relates to a plated article having a metal thin film formed by electroless plating, and to a method for manufacturing the plated article.
In particular, the present invention relates to a plated article in which a metal thin film is formed by electroless copper plating as a seed layer in forming ULSI ultrafine copper wiring (damascene copper wiring), and to a method for manufacturing the plated article.
2. Description of the Related Art
Electroless copper plating holds the promise of superseding current methods, such as sputtering and copper electroplating, as a method for forming copper films in ULSI ultrafine copper wiring (damascene copper wiring).
It has been difficult to achieve sufficient adherence in a deposited plating film when electroless copper plating is carried out on mirror surfaces such as that of a semiconductor wafer. It has also been difficult to carry out uniform plating over the entire surface of a substrate, on account of low plating reactivity. Other problems have been the difficulty of achieving uniform plating, and the lack of sufficient adherence, when forming a copper seed layer by electroless plating on a barrier metal layer such as tantalum nitride.
The inventors had already found that the plating deposition rate can be slowed down and crystals become extremely fine, allowing a thin film having a uniform thickness of no greater than 15 nm to be formed on a mirror surface such as a wafer. This can be achieved by preparing an electroless copper plating solution with an additive of a water-soluble nitrogen-containing polymer having a small weight-average molecular weight (Mw), preparing a substrate to be plated by causing a catalyst metal to adhere thereto or by forming a catalyst metal film on the outermost surface of the substrate, and immersing the substrate in the plating solution to cause adhesion of the polymer onto the catalyst metal via nitrogen atoms (Japanese Patent Application No. 2007-064348). Furthermore, in a working example of the above invention, the inventors showed that the plating deposition rate can be slowed down, and the crystals become extremely fine, allowing a thin film having a uniform thickness of no greater than 6 nm to be formed on a mirror surface such as that of a wafer, by forming beforehand a catalyst metal film on the outermost surface, followed by immersing the substrate in a plating solution to cause adhesion of a polymer onto the catalyst metal via nitrogen atoms.
In damascene copper wiring of the above method, when providing a copper seed layer by electroless plating after formation of a catalytic metal layer, a barrier layer aside from the catalytic metal layer should be formed beforehand for the prevention of copper diffusion. This means that a bilayer of the barrier layer and the catalytic metal layer needs to be formed prior to the copper seed layer formation. This has turned out to be problematic in terms of applicability to actual processing of ultrafine wiring, where the film thickness cannot be great.